[SI-LIST] Re: what's de-emphasis
- From: Istvan Novak <istvan.novak@xxxxxxx>
- To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
- Date: Mon, 02 Nov 2009 18:53:13 -0500
Lee and all others, who pointed out my typo off line.
Thanks for the correction. Yes, the first listed below is pre-emphasis,
the second listed is de-emphesis.
Regards,
Istvan
Lee Ritchey wrote:
> Istvan,
>
> Well put. For accuracy, the first is preemphasis.
>
> Lee
>
>
>
>> [Original Message]
>> From: Istvan Novak <istvan.novak@xxxxxxx>
>> To: Adiu <adiu_panli@xxxxxxxxx>
>> Cc: LY <long.0.yang@xxxxxxxxx>; Bill Wurst <billw@xxxxxxxxxxx>; prasad
>>
> <hariprasad.palli@xxxxxxxxx>; <Joseph.Schachner@xxxxxxxxxx>;
> <si-list@xxxxxxxxxxxxx>
>
>> Date: 11/2/2009 5:45:58 AM
>> Subject: [SI-LIST] Re: what's de-emphasis
>>
>> Adiu,
>>
>> In terms of resulting waveform shapes, preemphasis and deemphasis in
>> SerDes are identical. The differentiator is what is your baseline: if
>> your reference level is the steady state and you boost the first
>> transition bit, it is called deemphasis. If the level of your first
>> transitioning bit is the reference and you decrease the level of
>> subsequent bits, it is called deemphasis. The difference matters only
>> for the cell design, for the user they should be identical.
>>
>> Regards,
>>
>> Istvan Novak
>> SUN Microsystems
>>
>>
>>
>>
>> Adiu wrote:
>>
>>> Thanks for all replies.
>>>
>>> My application of this pre/de-emphasis is SerDes signals.
>>> It is more clear to me now that pre/de-emphasis functions similarly
>>> (the pulse waveform shape looks same), except that de-emphasis
>>> produces smaller amplitude.
>>>
>>> However, going to the implementation details, I still have some
>>>
> concerns.
>
>>> To explain my concerns more clearly, I am attaching a one-page word
>>> document.
>>> In the document,
>>> First, an arbitrary 1v nominal waveform is shown.
>>> Second, the pre-emphasis implementation block digaram captured from a
>>> Altera document is shown.
>>> Third, the pre-emphasis waveform obtained based on the Altera
>>> implementation diagram is shown. my concern: this waveform seems to me
>>> more like the de-emphasis waveforms based on the dicussion.
>>> Fourth, I try to plot the pre-emphasis waveform based on the
>>> discussion. my concern: is this correct?
>>>
>>> Could any one provide me the block implementation diagrams for both
>>> pre-emphasis and de-emphasis?
>>>
>>> Thanks again for everyone's time.
>>>
>>> Best regards,
>>> Adiu
>>>
>>> --- On *Sun, 11/1/09, Istvan Novak /<istvan.novak@xxxxxxx>/* wrote:
>>>
>>>
>>> From: Istvan Novak <istvan.novak@xxxxxxx>
>>> Subject: Re: [SI-LIST] Re: what's de-emphasis
>>> To: "LY" <long.0.yang@xxxxxxxxx>
>>> Cc: "Bill Wurst" <billw@xxxxxxxxxxx>, "Adiu"
>>> <adiu_panli@xxxxxxxxx>, "prasad" <hariprasad.palli@xxxxxxxxx>,
>>> Joseph.Schachner@xxxxxxxxxx, si-list@xxxxxxxxxxxxx
>>> Received: Sunday, November 1, 2009, 10:25 PM
>>>
>>> If you search the SI-list archives you should find past
>>> discussions on
>>> this same topic with more detailed explanations.
>>>
>>> LY wrote:
>>> > Istvan:
>>> > Could you make it clear about the pre/de-emphasis in
>>> > telecommunications and SerDes signaling?
>>> >
>>> > Long Yang
>>> > Joan Crawford - "I, Joan Crawford, I believe in the dollar.
>>> > Everything I earn, I spend." -
>>> > http://www.brainyquote.com/quotes/authors/j/joan_crawford.html
>>> >
>>> >
>>> > On Mon, Nov 2, 2009 at 08:13, Istvan Novak <istvan.novak@xxxxxxx
>>> <http://ca.mc354.mail.yahoo.com/mc/compose?to=istvan.novak@xxxxxxx>>
>>> wrote:
>>> >
>>> >> Bill and All,
>>> >>
>>> >> Rather than saying that this definition is wrong, we should say
>>> that
>>> >> this does not apply to digital SerDes signaling.
>>> >> If one reads the entire text on wikipedia, it is clear that it
>>> refers to
>>> >> telecommunications applications, where the high-
>>> >> frequency components are in fact suppressed. The unfortunate
>>> fact is
>>> >> that deemphasis means different things in
>>> >> telecommunications and in SerDes signaling.
>>> >>
>>> >> Regards,
>>> >>
>>> >> Istvan Novak
>>> >> SUN Microsystems
>>> >>
>>> >>
>>> >> Bill Wurst wrote:
>>> >>
>>> >>> Adiu,
>>> >>>
>>> >>> As Joe S. indicated, the definition for de-emphasis is clearly
>>> wrong. A
>>> >>> more correct way of stating de-emphasis would be:
>>> >>> De-emphasis: Improving the signal to noise ratio by
>>> >>> decreasing the magnitude of lower frequency signals
>>> >>> with respect to higher frequency signals.
>>> >>> Even with this corrected definition, you will note that what
>>>
> both
>
>>> >>> pre-emphasis and de-emphasis accomplish is similar. Thus,
>>> given the
>>> >>> same input waveshape, the waveforms output from either process
>>> will have
>>> >>> the same shape.
>>> >>>
>>> >>> Either pre-emphasis or de-emphasis is usually accomplished at
>>>
> the
>
>>> >>> transmitter, while equalization is done at the receiver.
>>> Although all
>>> >>> three work in different ways, they all accomplish the same
>>> purpose,
>>> >>> i.e., to flatten the frequency response of the overall system by
>>> >>> compensating for distortions introduced by the transmission
>>> medium.
>>> >>>
>>> >>> Best regards,
>>> >>> -Bill
>>> >>>
>>> >>> /************************************
>>> >>> / William C. Wurst, PE /
>>> >>> / billw@xxxxxxxxxxx
>>> <http://ca.mc354.mail.yahoo.com/mc/compose?to=billw@xxxxxxxxxxx>
>>> /
>>> >>> / Advanced Electronic Concepts, LLC /
>>> >>> / www.aec-lab.com /
>>> >>> ************************************
>>> >>> =========================================================
>>> >>> prasad wrote:
>>> >>>
>>> >>>
>>> >>>> i believe, its a matter of reference with which we are
>>> defining. since the
>>> >>>> technique is much evident when we see frequent transitions,
>>> the amplitude of
>>> >>>> those bits is higher than the bits having the lesser
>>> transitons. extending
>>> >>>> this to a combination of lets say, 0111, the transtion from 0
>>> to 1 will have
>>> >>>> higher amplitude than the further 1s. so we say that 0to 1 is
>>> pre emphasized
>>> >>>> or 1to 1 is deemphasized w r t 0 to 1.
>>> >>>>
>>> >>>>
>>> >>>>
>>> >>>> 2009/10/31 <Joseph.Schachner@xxxxxxxxxx
>>>
>>>
> <http://ca.mc354.mail.yahoo.com/mc/compose?to=Joseph.Schachner@xxxxxxxxxx>>
>
>>> >>>>
>>> >>>>
>>> >>>>
>>> >>>>> Of the two definitions you got from Google:
>>> >>>>> Pre-emphasis: " Improving the signal to noise ratio by
>>> increasing the
>>> >>>>> magnitude of higher frequency signals with respect to lower
>>> frequency
>>> >>>>> signals"
>>> >>>>> De-emphasis: " Improving the signal to noise ratio by
>>> decreasing the
>>> >>>>> magnitude of higher frequency signals with respect to lower
>>> frequency
>>> >>>>> signals"
>>> >>>>>
>>> >>>>>
>>> >>>>> The Pre-emphasis definition is acceptable. The De-emphasis
>>> definition is
>>> >>>>> clearly wrong, in my opinion. De-emphasis goal is the same,
>>> to increase
>>> >>>>> magnitude of higher frequency signals with respect to low
>>> frequency
>>> >>>>> signals. It just is a slightly different way to get that
>>> effect.
>>> >>>>>
>>> >>>>> I think pre-emphasis and de-emphasis are much easier to
>>> understand in the
>>> >>>>> time domain, rather than the frequency domain.
>>> >>>>> In the time domain, as text with with one dash per UI
>>> (transitions don't
>>> >>>>> appear) :
>>> >>>>> Each diagram is 4 UI low, 5 UI high, 4 UI low
>>> >>>>> _
>>> >>>>> _____ ... ____ ... _
>>> >>>>> ____
>>> >>>>> ____ ____ ... ____ ___ ... ____ ___
>>> >>>>> _ _
>>> >>>>>
>>> >>>>> The desired pulse With pre-emphasis With deemphasis
>>> >>>>> The first UI All but the first UI
>>> >>>>> after a transition after a transition
>>> >>>>> is higher amplitude are lower amplitude
>>> >>>>>
>>> >>>>>
>>> >>>>> The reason to do this is because a normal channel attenuates
>>> high
>>> >>>>> frequencies more,
>>> >>>>> so the (relatively) sharp rising edge of a transmitted pulse
>>> will become
>>> >>>>> slower
>>> >>>>> at the far end, and the first UI would not reach the desired
>>> height by the
>>> >>>>> middle
>>> >>>>> of the UI. That is, it would cause the eye opening to be
>>> reduced.
>>> >>>>> By having the TX pump out a larger transition, after the
>>> loss due to the
>>> >>>>> channel,
>>> >>>>> at the far end, the signal looks better - more like what we
>>> desired.
>>> >>>>> Standards
>>> >>>>> like PCI-Express don't actually call for pre-emphasis,
>>> rather they call for
>>> >>>>> de-emphasis. The effect is the same - the transitions are
>>> sent larger than
>>> >>>>> subsequent bits; but it is achieved by using the nominal
>>> level for the
>>> >>>>> first bit
>>> >>>>> after a transition and a smaller level for all subsequent
>>> bits. This makes
>>> >>>>> a nice
>>> >>>>> but smaller eye.
>>> >>>>>
>>> >>>>> --- Joe S.
>>> >>>>>
>>> >>>>>
>>> >>>>> Adiu wrote:
>>> >>>>>
>>> >>>>>
>>> >>>>>> Hello, Everyone
>>> >>>>>>
>>> >>>>>> What's pre-emphasis and de-emphasis?
>>> >>>>>> I can get the following definitions from Google:
>>> >>>>>>
>>> >>>>>> Pre-emphasis: " Improving the signal to noise ratio by
>>> increasing the magnitude of higher frequency signals with respect
>>> to lower frequency signals"
>>> >>>>>> De-emphasis: " Improving the signal to noise ratio by
>>> decreasing the magnitude of higher frequency signals with respect
>>> to lower frequency signals"
>>> >>>>>>
>>> >>>>>> There is not problem to understand the above definitions.
>>> However, I have difficulities in the following concerns:
>>> >>>>>> 1. is pre-emphasis always at the transmitter?
>>> >>>>>> 2. is de-emphasis always at the receiver?
>>> >>>>>> 3. what's difference between de-emphasis and equalization?
>>> >>>>>> 4. I have not problems to draw the pre-emphasis pulse
>>> waveforms with respect to a normal waveform. However, I am not
>>> quite sure of the de-emphasis pulse waveforms. The attached figure
>>> shows a simple example. Could someone confirms for me if the
>>> waveforms are draw correctly?
>>> >>>>>>
>>> >>>>>> any comments are appreciated.
>>> >>>>>>
>>> >>>>>> best regards,
>>> >>>>>> adiu
>>> >>>>>>
>>> >>>>>>
>>> >>
>>>
> -----
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